Watercraft with sterndrive and hull with vented tunnel

ABSTRACT

A watercraft includes a sterndrive comprising an inboard engine and an outdrive that extends through the transom. The aft end of the hull includes a stepped tunnel, which allows the sterndrive propellers (or other drives) to be operated at a relatively higher position in the water, without unduly decreasing the propeller performance. The stepped tunnel is vented to atmospheric pressure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Application No.62/101,748, filed Jan. 9, 2015, the entire disclosure of saidapplications is hereby incorporated by reference herein.

BACKGROUND

The three most common types of drive systems for powered watercraft are(i) outboard drives wherein the engine and drive unit are located offthe aft end of the watercraft, (ii) inboard drives wherein the engineand transmission are located inboard and configured to power a propellerdriveshaft that typically extends through and under the hull, and (iii)sterndrives or I/O drives wherein an engine is located inboard on thewatercraft, typically near the transom, and a drive unit, referred to asan outdrive, extends through the transom with a gear box disposedoutboard of the transom.

The original conception of the sterndrive has been attributed to CharlesStrang as described by Jeffrey L. Rodengen in “Iron Fist: The Lives ofCarl Kiekhaefer” (1990). The first patent disclosing a sterndrive isU.S. Pat. No. 3,376,842, to J. R. Wynne, which is hereby incorporated byreference in its entirety. The first commercial embodiment of asterndrive watercraft was the Aquamatic™, introduced by Swedish enginecompany Volvo Penta in 1959.

In a sterndrive the drive unit, or “outdrive,” transmits power from aninboard engine through the transom and downward to a propeller below thewaterline. The outdrive typically includes an upper subassemblycomprising a driveshaft that connects the inboard engine to an uppergear box through the transom, and a lower subassembly connected to theupper gear box to a lower gear box that drives the propeller shaft.

A common problem with powered watercraft, and in particularhigh-performance watercraft operated in shallow waters such as thelittoral zone and in rivers, is the risk of damage to the drivecomponent, for example, the propeller(s) or water jet outdrives(sometimes referred to herein as a jet pump), and related components dueto contact with the ground. Such risk is mitigated if the drivecomponent can be operated higher in the water. Higher positioning of thepropellers or other drive components would also enable the watercraft tosafely operate in shallower waters, and would reduce the hydrodynamicdrag.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

A watercraft includes a hull having a transom, wherein the hull definesa downwardly open, stepped tunnel on the aft end of the hull. Thewatercraft further includes an inboard engine and an outdrive assembly.The outdrive assembly extends from the inboard engine, through thetransom, and is drivably connected to a propeller or jet pump to providemotive power to the watercraft, wherein the propeller or pump isdisposed aft of the stepped tunnel. A vent provides a flow path from thestepped tunnel to an atmospheric vent port.

In an embodiment the outdrive assembly includes (i) a first drive shaftdrivably connected to the inboard engine and extending through thetransom, (ii) an upper gearbox disposed outboard of the transom thatengages the first drive shaft, (iii) a second drive shaft that engagesthe upper gear box and extends downwardly, and (iv) a lower gear boxthat engages the second drive shaft, wherein the propeller or jet pumpare drivably connected to the lower gear box.

In an embodiment the stepped tunnel has a maximum width that is between25% and 60% of the hull beam.

In an embodiment the tunnel length is between 10% and 25% of a length ofthe hull.

In an embodiment the vent includes a plurality of channels, each channelhaving a first port near the step.

In an embodiment the outdrive is configured such that during operationthe propeller or jet pump is positioned to draw water from the steppedtunnel.

In an embodiment the outdrive is pivotable to move the propeller of jetpump between a lower positon in the water and an upper position out ofthe water.

In an embodiment the stepped tunnel extends along less than half thehull length overall.

In an embodiment the propeller or jet pump comprises one or morepropellers.

In an embodiment the hull is a Vee hull and comprises outboardstabilizing members mounted to hull side sheets.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a watercraft in accordance with thepresent invention;

FIG. 2A is a side view of the watercraft shown in FIG. 1;

FIG. 2B is a diagrammatic side view of the watercraft shown in FIG. 1,illustrating the aft vented tunnel in the hull;

FIG. 3 is an upper perspective view of the aft end of the watercraftshown in FIG. 1; and

FIG. 4 is a lower perspective view of the aft end of the watercraftshown in FIG. 1.

DETAILED DESCRIPTION

A particular embodiment of a watercraft in accordance with the presentinvention will be described to assist in understanding the presentinvention. It will be readily apparent to persons of skill in the artthat the invention is not limited to the details of the currentembodiment, and the teachings herein may be readily applied to a broadrange of watercraft.

A perspective view of a watercraft 100 in accordance with the presentinvention is shown in FIG. 1. A starboard side view of the watercraft100 is shown in FIG. 2A. In this exemplary embodiment the watercraft 100includes a rigid planing hull 102. For example, the planing hull 102 maybe a deep V-hull (sometimes referred to as a vee hull). The hull 102includes a pair of curved side sheets 103 that join at a forward end toform a bow 104. The side sheets 103 engage a transom 106 at an aft end.An optional and conventional cabin 110 is also shown. An inboard enginecompartment 108 enclosing an engine 122 (see FIG. 2B) is located aft ofthe cabin 110, near the transom 106. In a current embodiment the engine122 is a conventional diesel or gasoline internal combustion marineengine, but alternative engine means are contemplated, including anysuitable power plant, including, for example, electric, hybrid, or fuelcell powered motors. In this embodiment, the watercraft 100 furthercomprises an optional deck extension 114 that extends aft from thetransom 106, and outboard stabilizing members or sponsons 112 mounted tothe hull side sheets 103.

The inboard engine 122 is drivably connected to an outboard drive trainor outdrive assembly 124. The outdrive assembly 124 extends from theengine 122, through the transom 106, and downward into the water to turnone or more (two shown) propellers 129 that drive the watercraft 100through the water. Other drive means, for example, a jet pump or thelike, may alternatively be use. The inboard engine 122 and outdriveassembly 124 are collectively referred to as an I/O drive or sterndrive120. An exemplary sterndrive is disclosed in U.S. Pat. No. 8,070,540, toWest et al., which is hereby incorporated by reference.

Refer now also to FIG. 2B, which shows a simplified starboard side viewof the watercraft 100, and illustrating a venting system in dashed line.Refer also to FIG. 3, which shows a lower perspective view of the aftend of the watercraft 100, including details of the outdrive assembly124. The outdrive assembly 124 includes an upper portion comprising afirst driveshaft 121 that extends through the transom 106, and connectsthe engine 122 to an upper gearbox 123U located outboard of the transom106. A second driveshaft 127 connects the upper gearbox 123U to a lowergearbox 123L. Typically the gearboxes 123U, 123L are 90-degreegearboxes. A propeller shaft 126 is driven from the lower gearbox 123L.In sterndrive systems the watercraft 100 is typically steered bypivoting the outdrive assembly 124 laterally (similar to an outboardwatercraft). As in an outboard motor, no rudder is needed. The outdriveassembly 124 includes a mechanism, for example, one or more hydraulicactuators 119 for pivoting the outdrive assembly 124 upwardly fortrailering or when the sterndrive is not in use, to avoid damage to theoutdrive assembly 124. The outdrive assembly 124 may optionally bepivotable from a lower positon to an upper position, for example, whenthe watercraft is in very shallow water, to protect the outdriveassembly 124 from damage in the event of beaching.

A problem with conventional marine outdrive systems, includingsterndrives, is that for acceptable performance the propeller(s) 129must extend deep enough into the water to engage relatively “clean”water. The propellers 129 are near the aft end of the hull 102, and drawwater from beneath the hull 102. Propellers in conventional stern drivesystems are therefore positioned below the lowermost edge of the hull.The low position of the drive component increases the risk of damage tothe drive system, limits the minimum safe operating depth for thewatercraft, and increases the drag on the watercraft. The deeper thepropellers 129 are positioned during operating, the more susceptiblethey are to damage from objects protruding from the waterbed. The riskto the propeller is compounded in high-performance watercraft that areconfigured to operate in a planing configuration because rotating thehull to the planing angle moves the propellers 129 deeper into thewater.

The hull 102 of the watercraft 100 disclosed herein includes a short,stepped tunnel 130 at the aft end of the hull 102. The aft steppedtunnel 130 is positioned directly forward of the outdrive propellers129. The stepped tunnel 130 allows the propellers 129 to be mountedhigher in the water without encountering interference from the hull 102because the stepped tunnel 130 provides a flow path for water to thepropellers 129. The stepped tunnel 130 is short and narrow as discussedbelow, and therefore the outboard portions of the hull 102 adjacent thetunnel 130 provide desired buoyancy for the watercraft 100.

However, under conventional design practices it is counterintuitive toinclude a stepped tunnel on the aft end of a high-performance watercraftbecause a stepped tunnel will reduce hull performance. According to theBernoulli principle, as the speed of a moving fluid increases, thepressure within the fluid decreases. During moderate- to high-speedoperation of a watercraft having a stepped aft tunnel, water flowingthrough the stepped tunnel accelerates, generating a significant vacuumor low-pressure region in the tunnel. The vacuum pressure is veryundesirable because low pressure in the tunnel pulls the hull deeperinto the water, thereby increasing drag, thereby decreasing hullperformance. Moreover, as the hull moves deeper into the water thepropellers or jet pump nozzles also move deeper into the water, wherethey are more susceptible to damage.

In order to prevent the undesirable low-pressure region in the afttunnel 130 region, the aft tunnel 130 in the present invention is ventedto a location above the waterline, to maintain atmospheric pressure inthe tunnel 130. Refer now also to FIG. 4 and FIG. 2B, which shows alower perspective view of the aft end of the watercraft 100. The forwardend of the stepped tunnel 130 is configured with one or more vents 131extending between lower vent ports 132 (three shown) that open into thestepped tunnel 130 and atmospheric vent ports 134 that opens toatmospheric pressure above the waterline. For example, in thisembodiment the lower vent ports 132 are fluidly connected to atmosphericvent ports 134 in the transom 106. Alternatively, the atmospheric ventports 134 may be positioned on the side sheets 103 or in the deck, forexample, into the engine compartment 108.

Therefore during operation of the watercraft 100 the pressure in thestepped tunnel 130 is maintained substantially at atmospheric pressure.

The stepped tunnel 130 in the current exemplary embodiment has a widthbetween 25% and 60% of the watercraft 100 hull beam (conventionallydefined as the maximum width of the hull 102). It is contemplated thatin some applications the watercraft may have twin sterndrive 120 systemsinstalled side by side (or more than one outdrive assembly 124 driven bya single engine 108). In the embodiment shown in FIG. 1 the steppedtunnel 130 is about 44% of the beam. In multi-drive configurations, itmay be desirable for the stepped tunnel 130 to be wider than 60% of thewatercraft beam. Alternatively, it is contemplated that separate shorttunnels similar to short tunnel 130 may be provided for each outdriveassembly 124.

The short tunnel 130 in the current embodiment has a length that isbetween 10% and 25% of the length overall (conventionally defined as themaximum length of the hull 102 measured parallel to the waterline, andoften abbreviated LOA), and in the current embodiment is about 15% ofthe hull length overall.

As discussed above, the vented aft stepped tunnel 130 allows thesterndrive and, in particular, the outdrive assembly 124 to be mountedhigher on the transom, such that the propeller 129 (or jet pumps) may belocated higher in the water, without significantly impacting theperformance or other desirable properties of the hull. This provides thebenefits of reducing drag and increasing performance and fuelefficiency. The higher mounting also reduces the risk of damage to thepropeller or jet pump drive system, allowing the watercraft 100 tooperate in shallow water. A higher propeller location also furtherprotects the propeller when the outdrive 124 is pivoted upwardly fortrailering, or for protection for example, in shallow waters.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. A watercraft comprising: a hull having a transom, wherein the hulldefines a downwardly open stepped tunnel on an aft end of the hull, thestepped tunnel having a forward end defining a step and an open aft end;an inboard engine; an outdrive assembly extending from the inboardengine, through the transom, and drivably connected to a propeller orjet pump to provide motive power to the watercraft; and a vent thatprovides a flow path from the stepped tunnel to an atmospheric ventport, wherein the propeller or jet pump is disposed directly aft of thestepped tunnel.
 2. The watercraft of claim 1, wherein the outdriveassembly comprises (i) a first drive shaft drivably connected to theinboard engine and extending through the transom, (ii) an upper gearboxdisposed outboard of the transom that engages the first drive shaft,(iii) a second drive shaft that engages the upper gear box and extendsdownwardly, and (iv) a lower gear box that engages the second driveshaft, wherein the propeller or jet pump are drivably connected to thelower gear box.
 3. The watercraft of claim 1, wherein the stepped tunnelhas a maximum width that is between 25% and 60% of the hull beam.
 4. Thewatercraft of claim 1, wherein the stepped tunnel has a length between10% and 25% of the hull length overall.
 5. The watercraft of claim 1,wherein the vent comprises a plurality of channels, each channel havinga first port near the step and an atmospheric port.
 6. The watercraft ofclaim 1, wherein the outdrive assembly is configured such that duringoperation the propeller or jet pump is positioned to draw water from thestepped tunnel.
 7. The watercraft of claim 1, wherein the outdriveassembly is pivotable to move the propeller or jet pump between a lowerposition wherein the propeller or jet pump is disposed directly aft ofthe stepped tunnel, and an upper position wherein the propeller or jetpump is disposed away from the stepped tunnel.
 8. The watercraft ofclaim 1, wherein the stepped tunnel extends along less than half thehull length overall.
 9. The watercraft of claim 1, wherein the propelleror jet pump comprises one or more propellers.
 10. The watercraft ofclaim 1, wherein the hull comprises a deep vee-hull.
 11. The watercraftof claim 1, wherein the hull further comprises outboard stabilizingmembers mounted to hull side sheets.
 12. A watercraft comprising: a veehull having a transom and oppositely disposed side sheets, wherein thehull defines a downwardly open stepped tunnel having a forward enddefining a step and an open aft end; an inboard engine disposed in anengine compartment near the transom; an outdrive assembly comprising (i)a first drive shaft drivably connected to the inboard engine andextending through the transom, (ii) an upper gearbox disposed outboardof the transom that engages the first drive shaft, (iii) a second driveshaft that engages the upper gear box and extends downwardly, (iv) alower gear box that engages the second drive shaft, and (v) a propelleror jet pump drivably connected to the lower gear box; and a vent thatprovides a flow path from the stepped tunnel to an atmospheric ventport; wherein the propeller or jet pump is disposed directly aft of thestepped tunnel.
 13. The watercraft of claim 12, wherein the steppedtunnel has a maximum width that is between 25% and 60% of the hull beam.14. The watercraft of claim 12, wherein the stepped tunnel has a lengthbetween 10% and 25% of the hull length overall.
 15. The watercraft ofclaim 12, wherein the vent comprises a plurality of channels, eachchannel having a first port near the step and an atmospheric port. 16.The watercraft of claim 12, wherein the outdrive assembly is pivotableto move the propeller or jet pump between a lower position wherein thepropeller or jet pump is disposed directly aft of the stepped tunnel,and an upper position wherein the propeller or jet pump is disposed awayfrom the stepped tunnel.
 17. The watercraft of claim 12, wherein thestepped tunnel extends along less than half the hull length overall. 18.The watercraft of claim 12, wherein the propeller or jet pump comprisesone or more propellers.
 19. The watercraft of claim 12, wherein the hullfurther comprises outboard stabilizing members mounted to hull sidesheets.